1. Field of the Invention
The present invention relates to a single-panel type color liquid crystal display apparatus to be used for example as a compact projection type color liquid crystal television system or a thin color information display apparatus. The single-panel type liquid crystal display device conducts a color display by means of one liquid crystal display device, without using a mosaic-like color filter.
2. Description of the Related Art
Projection type display methods for displaying color images are categorized into a so-called single-panel method, in which a single liquid crystal display device is used, and a three-panel method, in which three liquid crystal display devices corresponding to the three primary colors are used.
According to the single-panel method, a color filter of a mosaic-like or stripe-like configuration, designed to correspond to the respective pixels included in a liquid crystal display device, is used. An example of a single-panel method is disclosed in Japanese Laid-Open Patent Publication No. 59-230383. This method has an advantage in that the configuration of the optical system may be simple, and that only a liquid crystal display device is used, thereby allowing the entire system to be compact. However, according to this method, about 2/3 of light irradiated onto the liquid crystal display device is absorbed or reflected by the color filter, thereby decreasing the brightness of the displayed image.
On the other hand, according to the three-panel method, a light beam is separated into the three primary colors, i.e., red, green, and blue, by using a wavelength selection element. An optical system for transmitting the light beam of each primary color, and three liquid crystal display devices for forming images by controlling the light beams of the respective colors are used, so as to conduct color display by optically overlaying the images of the respective primary colors. An example of a three-panel method is disclosed in Japanese Laid-Open Patent Publication No. 60-169827. This method has an advantage in that the emitted light beams can be utilized at high efficiency, so that images of brightness of about three times as high as that of images by the single-panel method can be obtained. However, this method is more disadvantageous, in terms of cost and compactness, than the single-panel method because it requires a larger number of component elements.
A method for solving the above-mentioned problems of the single-panel method and the three-panel method is proposed in Japanese Laid-Open Patent Publication No. 4-60538. In a first example of this proposal, a white light beam emitted from a light source is separated into light beams of red, blue, and green by means of dichroic mirrors disposed in a fan-shaped arrangement. The light beams are incident, at their respective incident angles different from each other, on a microlens array of a lenticular shape disposed by the light source side of a simple matrix type liquid crystal display device incorporating stripe-shaped electrodes. The microlens array has a semicylindrical shape extending along a vertical direction (e.g., a longitudinal direction) of the display of the liquid crystal display device. The pitch of the microlenses is equivalent to three pixels of the liquid crystal display device. The light beams of the wavelength bands of red, blue, and green are led through the microlenses at their respective incident angles so as to be incident on portions of the liquid crystal corresponding to their respective colors, and are subjected to optical modulation for each color in accordance with an image signal. The light beams which have passed through the liquid crystal portions are converged onto an aperture of a projection lens by a field lens provided for preventing the light beams from being diffused to the peripheral portions. Thus, a color image is projected.
The method according to the above proposal has an advantage, as compared to the two methods mentioned above, in that no absorption of light occurs because no color filter is used, thereby providing a color image of a brightness of about three times as high as that of an image obtained by the conventional single-panel method. This method is also advantageous in terms of cost and compactness because, being a single-panel method, the number of the component elements can be smaller than in the case of a three-panel method.
Furthermore, a second example of the above-mentioned proposal discloses a combination of an active matrix liquid crystal display device including pixels disposed in a delta arrangement and hexagonal-shaped microlenses, which provides similar effects.
However, the single-panel method according to the above-mentioned proposal has the following problems (1) and (2). Problem (1) corresponds to the case where the method is applied to an active matrix type liquid crystal display device of a delta arrangement type, while problem (2) corresponds to the case where the method is applied to an active matrix type liquid crystal display device of a stripe arrangement type:
(1) The delta arrangement, which is a suitable arrangement of pixels for displaying television images, video images, and the like, requires a bus line of TFTs (Thin Film Transistors) in a crank-like shape so as to produce the active matrix type liquid crystal display device. The presence of such a crank-like portion leads to a decrease in the aperture ratio and the yield of the active matrix type liquid crystal display device (because of the difficulty in forming such a portion), thereby making this arrangement more disadvantageous than the stripe arrangement.
(2) In an active matrix type liquid crystal display device of a stripe arrangement type, pixels are arranged in a stripe-shape. According to the method of the above-mentioned proposal (single-panel method), light beams of different incident angles are distributed for liquid crystal portions corresponding to their respective colors by means of a microlens array of a lenticular shape. As a result, the light beams, when converged, form a stripe shape extending along the vertical direction. However, an active matrix type liquid crystal display device incorporates a black matrix of a lattice configuration between the pixels. As a result, the stripe-shaped light beams can pass only through the apertures of the pixels, and are interrupted in the other portions (such as the lattice portion of the black matrix). Therefore, there is a problem in that the screen illuminance is limited by the ratio of the aperture of the liquid crystal display device, which is determined in accordance with the ratio of the pitch of the pixels along the vertical direction to the size of the apertures.
The above-mentioned problems could be solved by, for example, providing an oblong microlens array which is longer horizontally than vertically, the lenticular lens layer being divided at the pixel pitch and having a curvature along the vertical direction as well as in the horizontal direction. In this case, the two functions of distribution of light beams along the horizontal direction and the conversion of light along the vertical direction are performed at the same time, so as to improve the ratio of the aperture.
In the above-mention case, each lens is oblong along the horizontal direction, so as to be long enough to extend to an equivalent of three pixels. However, microlenses may be formed by rounding the surface of a heated lens material by leaving the material in a fluid state so as to utilize the surface tension thereof, or by using such products as originals for producing replicas. In the case where the contour of the microlens is an oblong rectangular shape, a curved surface of a torus shape is obtained, resulting in a large astigmatism of the microlens. Moreover, a microlens produced by an ion exchanging method can also have astigmatism. In either case, the astigmatism of the microlens prevents any light from being converged into a small point. In order to converge light into one point, the lens surface must be spherical or axially symmetrical. However, a microlens produced by either of the above-mentioned methods has different curvatures along the vertical direction and the horizontal direction.